One of the most disarming scenes in RBG, a CNN documentary premiering September 3 on the cable network, is set at the U.S. Supreme Court Justice's gym. Her twice-weekly regime includes 20 pushups and exercises using a stretch band that, on this particular day, she deems too slack.

"This is light," she tells her trainer, who tightens the elastic so that Ginsburg, 85 years old and barely five-foot-one, has to flex harder.

"I couldn't believe it," says filmmaker Julie Cohen, who crouched in a corner with fellow director-producer Betsy West to observe Ginsburg in action. "There she was doing an exercise routine that, literally, I couldn't have done myself."

The oldest sitting justice and only the second woman to serve on the Supreme Court, Ginsburg — who marks 25 years in her post this August — has exploded in the public's consciousness in recent years. Hailed for her trenchant dissents and unwavering crusade for gender equality, the sober, unassuming justice has become a cultural icon.

Tumblrs, tattoos, tweets, raps, Instagrams and Halloween costumes all pay homage. Apple fashioned her likeness into a femoji. And there's no shortage of swag, including buttons, posters, T-shirts and baby onesies festooned with the moniker "Notorious RBG."

Still, West says, "We realized that a lot of her fans didn't know the whole story." In tracing Ginsburg's life, she and Cohen examine many of the landmark gender-equality cases that Ginsburg successfully argued before the Supreme Court prior to her confirmation in 1993.

"We wanted to bring those stories to life," West says. That meant interviewing plaintiffs such as Sharron Frontiero, whom Ginsburg represented in Frontiero v. Richardson, a 1973 case in which the Supreme Court decided that U.S. military benefits cannot be based on gender.

Viewers also get a glimpse into Ginsburg's private sphere, which included her late husband, Martin, whose wholehearted support extended to making sure she stopped to eat during protracted workdays. "This film is also the celebration of having the power of a feminist man in your life," Cohen says.

The filmmakers hired women for almost every significant function, including DP Claudia Raschke, editor Carla Gutierrez and composer Miriam Cutler. Courtney Sexton, vice-president of CNN Films, and Amy Entelis, executive vice-president of talent and content development for CNN Worldwide, served as executive producers.

"Collectively," Entelis says, "we brought a unique passion to this subject that enriched the project and brought out the sense of mission the justice seemed to have envisioned for her life more than 60 years ago."

Following its launch at Sundance earlier this year, RBG was released theatrically, becoming the highest-grossing film from Magnolia Pictures and Participant Media.

Throughout, Ginsburg appears unflappable. But no one can say she lacks humor. At one point, the filmmakers introduce her to Saturday Night Live, setting her up to watch Kate McKinnon's black-robed RBG impersonation, right down to the white lacy collars she favors.

As McKinnon lobs zingers (which she dubs "Ginsburns") and goofily dances, Ginsburg laughs. "It's marvelously funny," she remarks. Asked if she identifies with the characterization, she responds, "Not one bit." After a pause, she adds, "Except for the collar."